The reaction of bacterial bioluminescence is the luciferase catalyzed oxidation of reduced riboflavin 5'-monophosphate by molecular oxygen to produce an isolatable enzyme bound intermediate, which reacts with aliphatic aldehyde to produce light. The purpose of this research is to identify the chromophore which gives rise to the luminescence, this being crucial to the postulation of a reaction mechanism. A blue fluorescence protein of low molecular weight has been isolated and partially purified from extracts of luminous bacteria and this appears to be the light-emitting species. By the methods of affinity chromatography, gel electrophoresis and crystallization, this protein will be purified to homogeneity and then fully characterized with respect to molecular weight, hydrodynamic properties, composition and chromophore chemical structure. Preliminary results clearly distinguish it from the "light-inducible" form of luciferase. Spectral properties of blue fluorescence protein and of the separated chromophore will be determined by absorption, fluorescence emission and excitation, circular dichroism, fluorescence lifetime and quenching. An equilibrium model for a fluorescence shift accompanying a conformational change in the protein will be established. The interaction of blue fluorescence protein with bacterial luciferase will be investigated by methods of frontal analysis of gel chromatography, equilibrium centrifugation, fluorescence changes and circular dichroism. The result of these studies will be an increased understanding of the mechanism of interconversion of light and biological energy and also of details of the mechanism of enzyme catalyzed oxidation.